Video: Genetic Variability and Random Mutation

Evolution is driven by variation among populations. The amount of variability determines how well a population can adapt to environmental changes, while random mutations can provide new variations that help a population adapt to unexpected changes.2014-01-08

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Evolution is driven by variation among populations. The amount of variability determines how well a population can adapt to environmental changes, while random mutations can provide new variations that help a population adapt to unexpected changes.

Evolution Occurs Within Populations

The theory of evolution explains the phenomenon that species living today are descendants of species from long ago. A common misconception about this process is that individuals 'adapt' to their environment in order to survive, but this is not the case.

For example, a giraffe may want a longer neck so that it can reach leaves on higher branches, but it certainly can't make its neck grow longer to do so. However, other giraffes within the local population may naturally have longer necks, and if leaves on lower branches are in short supply, the shorter-necked giraffes within that population will not survive as well as the ones with longer necks. In this way, the population changes over time so that longer-necked giraffes are more common, and this reflects the demands of the environment (the higher branches).

So, it's in this way that evolution is more of an editing process than a creative process. There is no such thing as a 'perfect' organism. Evolution simply 'selects' for individuals with traits that are best suited to the current environment. If low branches become more available, the short-necked giraffes would thrive, since they are the ones within the population best suited for this type of environment.

Genetic Variability

Charles Darwin saw much evidence for evolution because he observed variation among individuals within populations, like the short- and long-necked giraffes. These differences are known as genetic variations, which are the naturally occurring genetic differences among individuals.

Variation is easy to see. For example, if your friend is looking for you in a crowd, they can easily spot you because you look different than everyone else. This comes from your unique DNA, which helps you look just a little bit different than all other humans. Even within your immediate family, you share many common traits, but each sibling will have their own variation on the genes inherited from your parents.

We can measure genetic variation, but what may be more important to understand is the potential for a characteristic to vary within a population, or the genetic variability. This is different from genetic variation because instead of measuring the actual variation within a population, it measures how much the trait will vary. Genetic variability is directly related to biodiversity and evolution, because a population needs enough variability to be able to adapt and evolve to environmental changes.

Let's look at our giraffe population as an example. The genetic variation in the population is the different length necks: short, long, and everything in between. The variability is how much that neck length tends to vary within the population. A high variability will allow the population to adapt to environmental changes (like the branch height), whereas a low variability means that population will not be able to adapt to new branch heights and will risk extinction.

Random Mutations

Some variations are hereditary, like neck length in giraffes. Long-necked giraffes will tend to have long-necked giraffe babies, while short-necked giraffes will tend to have short-necked babies. Sometimes, though, variations occur within a population because of random mutations, which are changes in the nucleotide sequence of DNA. Your DNA is like a set of instructions, and a mutation occurs when those instructions are changed.

Random mutations are a critical component of evolution because mutations create genetic variation within a population. If a mutation is harmful, it will likely be weeded out very quickly, because any change in the population that makes an organism less 'fit' will ultimately lead to its demise.

But sometimes a mutation may actually be beneficial to an individual, so it survives and reproduces, passing that variation on to the next generation. This often occurs when the environment is changing in such a way that it supports the mutation.

We see this with pesticide-resistant insects. All it takes is one individual to have a mutation in their genome that makes them resistant to pesticides, since they can survive and then pass this mutation on to their offspring. While most of the population may die after a pesticide application, the ones that have the resistance mutation will eventually become common, essentially creating a new population that is resistant to the poison.

Lesson Summary

Evolution occurs within a population because of variation among individuals. Genetic variation is when individuals in a population have variations of the same trait, such as short- or long-necked giraffes. The genetic variability of that population tells us how much the trait will vary. This also tells us how well that population will adapt to environmental changes: high variability means better adaptability, but low variability means a higher likelihood of extinction.

While many variations are hereditary (like a long-necked giraffe having long-necked babies), sometimes a variation comes about from a random mutation. This mutation occurs because of changes in an individual's DNA. Often, mutations are lethal because they are not beneficial to the individual. However, sometimes a mutation is beneficial, and this allows that individual to survive and create more offspring, making it more 'fit' for its environment.

Learning Outcomes

This lesson could provide you with the knowledge required to:

Cite an example of the theory of evolution

Explain the ways in which change occurs over time

Compare and contrast genetic variation and genetic variability

Discuss the occurrence and implications of random mutation in individuals

Summary:

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